Polyesters such as poly(ethylene terephthalate) (PET) are widely used in bottles and containers which are used for carbonated beverages, fruit juices, and certain foods. Useful polyesters have high inherent viscosities (I.V.) which allow the polyester to be formed into a parison and subsequently molded into a container. Because of the limited barrier properties with regard to oxygen, carbon dioxide and the like, PET containers are not generally used for products requiring long shelf life. For example, oxygen transmission into PET bottles that contain beer, wine and certain food products cause these products to spoil.
The preparation of polymer/clay nanocomposites containing for example, nylon-6 and alkyl ammoniun treated montmorillonite have been disclosed. However, most prior attempts used polyarnides due to their hydrogen bonding character and corresponding synergistic interaction with the negatively charged clay. The application of this technology to polyesters, particularly to improve barrier, has been limited due to the inability to achieve the required level of dispersion of the clay particles.
U.S. Pat. No. 4,889,885 discloses the polymerization of various vinyl monomers such as methyl methacrylate and isoprene in the presence of sodium montmorillonite. Example 11 describes the polycondensation of dimethyl terephthalate and ethylene glycol in the presence of 33 weight percent of a montmorillonite clay in water (for 6.2 final weight percent of clay in the polyester resin). However, the nanocomposite displayed only marginal improvement in barrier due to insufficient separation. Moreover, to achieve desirable molecular weights, the method used unacceptably long synthesis times to compensate for reduced condensation rates resulting from the high composite viscosity at low shear that occurs upon addition of the clay. In addition, the long exposure times to high-temperature during the polyester synthesis resulted in poor nanocomposite color.
WO 93/04117 and WO 93/04118 disclose the blending of up to 60 weight percent of intercalated clay materials with a wide range of polymers including polyamides, polyesters, polurethanes, polycarbonates, polyolefins, vinyl polymers, thermosetting resins and the like. Although the use of polyesters are disclosed as useful polymers and an example of a PET/Quat-Clay nanocomposite is providing in WO 93/04118, compositions prepared as described exhibit insufficient clay dispersion resulting in aesthetically poor composites. In addition, this method of preparation does not lead to improved barrier due to lack of separation.
U.S. Pat. Nos. 5,552,469 and 5,578,672 describes the preparation of intercalates derived from certain clays and water-soluble polymers such as polylvinyl pyrrolidone, polyvinyl alcohol, and polyacrylic acid. The specification describes a wide range of thermoplastic resins including polyesters and rubbers that can be used in blends with these intercalates. The disadvantages of this method are (1) poor thermal stability of the intercalant resin at PET processing temperatures causing extensive color and reactivity with the polyester resin, (2) poor compatibility with the polyester resin, (3) and insufficient contribution to barrier due to incomplete separation. The inability to contribute to barrier would not be predicted based on the disappearance of the d(001) montmorillonte X-ray defraction pattern as observed in FIG. 5 of U.S. Pat. No. 5,578,672.
JP Kokai patent no. 9-176461 discloses polyester bottles wherein the polyester contains swellable laminar silicate. WO 97/31057 discloses polymer composite having dispersed therein inorganic material such as clay which is separated with an inorganic intercalant. WO 97/31973 discloses a producing a composite material by mixing a potassium ionomer in which ethylene methacrylate copolymer is either partially or completely neutralized with an organic polymer. However, the foregoing references produce materials comprising very large tactoids and little if any dispersion of individual platelet particles. Nor do any of the references disclose nanocomposite compositions having other specific properties such as melt strength and viscoity and high I.V.
Thus there remains a need in the art for a process capable of introducing substantially separated platelet particles to polyesters to produce nanocomposites having improved barrier and good thermal stability.